An activist helping the Current TV reporters and their guide, who also was taken, says they may have ventured too close to the North Korean border while on a reporting trip in China.

BEIJING — At a time of escalating tensions on the Korean peninsula, two American TV journalists and their guide were taken into custody by North Korea while shooting video near the sensitive border region between China and the isolated state.

Laura Ling and Euna Lee were on assignment with San Francisco-based Current TV when they were seized Tuesday. The guide, whose name was not released, is a Chinese citizen.

Their detention was confirmed by activists who had helped arrange the reporting trip. The pair had been near the northeastern Chinese city of Yanji. It was unclear whether the Americans were on the Chinese or the North Korean side of the 850-mile border, which is marked by two rivers, the Yalu and the Tumen. Near Yanji, the Tumen is shallow enough at some stretches that people can wade through or walk across on winter ice, making for an active cross-border trade of smugglers, human traffickers and defectors.

"It is certain that the North Koreans have them," said Chun Ki-won, a South Korean pastor who spoke to the journalists by cellphone at 6 a.m. Tuesday, about an hour before their capture. "They must have gone in too close, where it was dangerous. I don't think the North Koreans would have dared to come out into China to kidnap Americans."

South Korea's YTN Television today quoted an unnamed source saying that the women might have crossed onto the North side unwittingly because recent drought had left river levels so low it was difficult to see the border. Another South Korean report said they were arrested after they refused to stop filming.

North Korea, one of the most xenophobic countries in the world, does not tolerate people trespassing across its borders. In 1996, an intoxicated American who swam naked across the Yalu River was held for three months on espionage charges before his release was negotiated by then-Rep. Bill Richardson of New Mexico.

North Korea could again try to use the Americans for political leverage. Its relations with the U.S. are particularly strained now because of Pyongyang's announcement that it intends to launch a satellite in early April. The U.S. and South Korea are also finishing military exercises in the region, an annual event that the North denounced this year as preparation for war.

Thousands of North Koreans cross the Chinese border every year to escape the chronic food shortages and oppression of the Pyongyang regime.

North Korean guards stationed along the river banks sometimes try to cadge cigarettes, candy and money from people visiting the area.

This is not the first time the North Korean guards have grabbed people at the border, but other cases -- involving Chinese or South Korean citizens -- haven't received much international attention.

At Current TV's San Francisco headquarters, a video editor who answered the telephone said the company had no comment.

Ling is the managing editor of "Vanguard," a weekly news show that features long-form pieces by a group of young correspondents. Its staff armed with hand-held digital cameras, the show advocates a "guerrilla-style approach" to journalism, its website says.

Euna Lee was reported to be a U.S. citizen of Korean origin. The guide is a Korean-speaking Chinese citizen.

Mitch Koss, an executive producer with Current TV who was with them, was able to flee and notify American officials of what had happened, according to Chun, the South Korean pastor.

The State Department said in a statement Thursday: "We are working with the Chinese government officials in the area to ascertain the whereabouts of the Americans in question. We also have been in touch with North Korean authorities to express our concern about the situation."